Power transfer assembly with planetary gearset having carrier with crack arresting features

ABSTRACT

A two-speed transfer case for a four-wheel drive vehicle is provided. The transfer case has a two-speed planetary gearset, a range clutch, and a range shift mechanism. The planetary gearset includes a carrier unit having at least one crack arresting feature configured to limit propagation of a stress crack. The carrier unit includes a plurality of mounting holes for securing planet gears for rotation relative to the carrier unit. The gearset includes a sun gear configured for and a ring gear, with the planet gears in meshed engagement with the sun gear and the ring gear. The crack arresting feature extends at least partially through a portion of the carrier unit and is configured to receive a crack propagating from a central aperture of the carrier unit. The crack arresting feature is disposed radially between the central aperture and the mounting holes.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of previously filed U.S.Provisional Patent Application, No. 62/722,298, filed Aug. 24, 2018, theentire content of which is hereby incorporated by reference in itsentirety.

FIELD

The present disclosure relates generally to power transfer systems forcontrolling the transmission of drive torque from a powertrain to adriveline of a motor vehicle. Such power transfer systems include powertransfer assemblies, such as multi-speed transmissions and transfercases, equipped with a planetary gearset for providing a speed reducingfunction. Specifically, the present disclosure relates to a carrier unitassociated with such a planetary gearset manufactured to include crackmitigating apertures configured to provide a “crack arresting” feature.

BACKGROUND

This section of the written disclosure provides background informationrelated to conventional power transfer systems of the type used in motorvehicles and is not necessarily prior art to the inventive conceptsdisclosed and claimed in this application.

Power transfer systems are utilized in four-wheel drive (4WD) motorvehicles for selectively directing power (i.e. drive torque) from thepowertrain to primary and secondary drivelines. In 4WD vehicles, thepower transfer system is usually configured to include a power splittingdevice, commonly referred to as a transfer case, arranged to normallytransmit drive torque to the primary/rear driveline and selectivelytransmit a portion of the total drive torque to the secondary/frontdriveline. Typically, such transfer cases include a rear output shaftinterconnecting the powertrain to the rear driveline, a front outputshaft interconnected to the front driveline, a transfer assemblydrivingly coupled to the front driveline, a mode clutch operablydisposed between the rear output shaft and the transfer assembly, and amode shift mechanism operable to shift the mode clutch between adisengaged condition and an engaged condition. With the mode clutchoperating in its disengaged condition, the transfer assembly isdisconnected from the rear output shaft so as to establish a two-wheeldrive mode. In contrast, the mode clutch is operable in its engagedcondition to drivingly connect the transfer assembly to the rear outputshaft so as to establish a four-wheel drive mode.

In “part-time” power transfer systems, the transfer case is equippedwith a dog-type positive-locking mode clutch and a mechanical mode shiftmechanism that can be actuated manually (i.e. via an operator-actuatedshift lever) or electrically (i.e. via an electric motor). Typically,such dog-type mode clutches include a mode sleeve splined for rotationwith the rear output shaft and which is axially moveable thereon via themode shift mechanism between disengaged and engaged positions withrespect to a clutch component coupled to the transfer assembly forrespectively shifting between the two-wheel drive mode and a “locked”four-wheel drive mode.

It is also known to use “on demand” power transfer systems forautomatically distributing drive torque from the powertrain to the frontand rear drivelines, without any input or action on the part of thevehicle operator, when a low traction condition is detected. Modernly,the on-demand feature is incorporated into transfer cases by replacingthe dog-type mode clutch and mechanical mode shift mechanism with amulti-plate friction clutch assembly and a power-operated clutchactuator that are interactively associated with an electric controlsystem and a sensor arrangement. During normal road and drivingconditions, the friction clutch assembly is maintained in a releasedcondition such that virtually all drive torque is transmitted to therear wheels via the rear driveline and the two-wheel drive mode isestablished. However, when the sensors anticipate or detect a lowtraction condition, the power-operated clutch actuator is actuated toengage the friction clutch assembly for transmitting a portion of thetotal drive torque to the front wheels via the front driveline, therebyestablishing an “on-demand” four-wheel drive mode. Examples of suchon-demand or “active” transfer cases are disclosed in U.S. Pat. Nos.8,091,451; 8,316,738; and 8,678,158.

To accommodate differing road surfaces and conditions, many transfercases are also equipped with a two-speed range unit, a range clutch anda range shift mechanism. The two-speed range unit typically includes aninput shaft directly driven by the powertrain, a planetary gearsethaving an input member driven by the input shaft and an output memberdriven at a reduced speed relative to the input member. The range clutchis usually a dog-type positive-locking range collar splined for rotationwith the rear output shaft and axially moveable thereon between a firstor high-range position coupled to the input member and a second orlow-range position coupled to the output member.

Typically, the planetary gearset includes a sun gear fixed to the inputshaft, a stationary ring gear, and a plurality of planet gears inconstant mesh with the sun gear and the ring gear. The planet gears arerotatably supported from a carrier unit. When the range clutch islocated in its high-range position, it functions to couple the sun gearto the rear output shaft for establishing a direct or high-ratio driveconnection therebetween. In contrast, when the range clutch is locatedin its low-range position, it functions to couple the carrier unit tothe rear output shaft for establishing a reduced or low-ratio driveconnection between the input shaft and the rear output shaft. Toestablish these drive connections, clutch teeth formed on the axiallymoveable range clutch move into and out of engagement with clutch teethformed on the sun gear (or the input shaft) and clutch teeth formed onthe carrier unit.

In many applications, the carrier unit is two-piece assembly having apair of interconnected laterally-spaced carrier plates with pinionshafts extending therebetween and on which the planet gears are mountedfor rotation. In other applications, the carrier unit is formed as aone-piece component, such as a powdered metal component, with the pinionshafts again used to rotatably support the planet gears. Typically, theclutch teeth are hardened to accommodate the cyclical loads and stressesgenerated upon engagement with the clutch teeth on the range clutch. Asis known, deflection of the rear output shaft causes high tooth stressat the carrier unit since partial clutch tooth engagement situationincreases such stresses. These high tooth stresses can, unfortunately,lead to cracks forming and propagating from the clutch teeth until thecarrier unit breaks and is no longer functional.

Thus, a need exists to develop carrier units for planetary gearsets ofthe type used in power transfer systems having a crack-arresting featureconfigured to inhibit and/or limit the growth of stress-related cracksso as to extend the service life of such carrier units during exposureto cyclical loading conditions.

SUMMARY

This section provides a general summary of the inventive conceptsassociated with this disclosure and is not intended to be interpreted asa complete and comprehensive listing of all of its aspects, objectives,features and advantages.

It is an aspect of the present disclosure to provide a power transferassembly for use in motor vehicle driveline applications which isequipped with a planetary gearset having a carrier unit with a crackarresting feature.

It is a related aspect of the present disclosure to configure the crackarresting feature as crack mitigating apertures that are formed in thecarrier unit in generally close proximity to a load bearing feature,such as spline and/or clutch teeth.

It is a further related aspect of the present disclosure to configurethe crack mitigating apertures as throughbores and/or partial depthindentations formed in/on the carrier unit.

It is an aspect of the present disclosure to provide a two-speedtransfer case for use in four-wheel drive vehicles equipped with a rangemechanism having a two-speed planetary gearset and a range clutch, and arange shift mechanism for shifting the range clutch.

In accordance with these and other aspects, the present disclosure isdirected to a planetary gearset comprising a sun gear, a ring gear, acarrier unit, and a plurality of planet gears rotatably supported by thecarrier unit and in constant meshed engagement with the sun gear and thering gear, wherein the carrier unit is formed to include a crackarresting feature configured to inhibit propagation of a stress crack.

The carrier unit includes teeth formed around an aperture, wherein thecrack arresting feature is located in close proximity to the teeth so asto inhibit propagation of a stress crack originating at one of theteeth.

The crack arresting feature may include a plurality of crack mitigatingapertures formed adjacent to the teeth. The crack mitigating aperturesmay be throughbores and/or partial depth bores formed in the carrierunit. The crack arresting apertures may be circular or lobe-shaped. Thecrack arresting apertures may be aligned along a common diameter and bespaced equally or in a staggered orientation. The crack arrestingaperture may include first and second pluralities of throughbores and/orpartial depth bores, with each of the first and second pluralities beingaligned respectively along a common first and second diameter.

The crack arresting feature may be in the form of arc-shaped aperturesor slots that extend partially or fully through the carrier ring of thecarrier unit. The arc-shaped apertures may have a radially inner end aradially outer end with a curvature defined therebetween. The arc-shapedapertures may be curved to correspond to the curvature of the mountingholes of the carrier unit that are disposed adjacent the arc-shapedapertures. The curvature may be concave in the radially outer directionand convex in the radially inner direction. The arc-shaped apertures maybe arranged on the carrier ring in the expected path of a crackpropagating from the teeth of the carrier unit, which may be determinedby FEA.

In view of these and other aspects, the present disclosure is directedto a two-speed transfer case configured to include: an input shaftadapted to receive drive torque from a powertrain; a rear output shaftadapted for connection to a rear driveline; a front output shaft adaptedfor connection to a front driveline; a transfer assembly drivinglyconnected to one of the front and rear output shafts, a two-speed rangemechanism operably disposed between the input shaft and the rear outputshaft; a range shift mechanism for controlling operation of thetwo-speed range mechanism; a mode mechanism operably disposed betweenthe transfer assembly and the other one of the front and rear outputshafts; and a mode shift mechanism for controlling operation of the modemechanism, wherein the range mechanism includes a planetary gearsetequipped with a carrier unit having crack arresting apertures.

In accordance with one non-limiting embodiment, the two-speed transfercase of the present disclosure includes a mode mechanism configured as amulti-plate friction clutch assembly, a mode shift mechanism configuredas a motor-actuated ballramp unit to control a clutch engagement forceapplied to the multi-plate friction clutch assembly, a range mechanismconfigured to include a planetary gearset and a positive-locking rangeclutch moveable between two range positions for establishing high-rangeand low-range drive connections, and a range shift mechanism configuredto include a range fork engaging the range clutch and having a followerretained in the guide slot formed in the range cam, and a shift operatorfor rotating the range cam to cause the follower to move within amulti-step range shift segment of the guide slot which causes the rangefork to axially move the range clutch between its high-range andlow-range positions.

In one aspect, a transfer case for a vehicle is provided, the transfercase comprising: a rotary input shaft operational at a first speed; arotary output shaft; a sun gear configured for concurrent rotation withthe rotary input shaft; a ring gear; a carrier unit; a planet gearrotatably supported by said carrier unit and in meshed engagement withsaid sun gear and said ring gear; a range mechanism configured to shiftbetween meshed engagement with the rotary input shaft to drive therotary output shaft at the first speed and meshed engagement with thecarrier unit to drive the rotary output shaft at a second speed; whereinsaid carrier unit is formed to include at least one crack arrestingfeature configured to inhibit propagation of a stress crack.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a schematic illustration of a four-wheel drive motor vehicleequipped with a power transfer system having a two-speed transfer caseconstructed in accordance with the teachings of the present disclosure;

FIG. 2 is a diagrammatical illustration of a two-speed active transfercase including a planetary gearset equipped with a carrier unit havingcrack arresting features which embody the teachings of the presentdisclosure;

FIG. 3 is a sectional view of a two-speed active transfer caseconstructed in accordance with a first embodiment;

FIG. 4 is a sectional view of a two-speed active transfer caseconstructed in accordance with a second embodiment;

FIG. 5 is a sectional view of a two-speed active transfer caseconstructed in accordance with a third embodiment;

FIG. 6 is a sectional view of a two-speed active transfer caseconstructed in accordance with a fourth embodiment;

FIG. 7 is an enlarged partial sectional view showing various componentsof the active mode clutch associated with the transfer cases shown inFIGS. 3 through 6;

FIG. 8 is a sectional view of a two-speed active transfer caseconstructed in accordance with a fifth embodiment;

FIG. 9 is a sectional view of a two-speed active transfer caseconstructed in accordance with a sixth embodiment;

FIG. 10 is an enlarged partial view illustrating the two-speed planetarygearset and range clutch associated with the transfer case shown in FIG.9;

FIG. 11 is an enlarged partial view of FIG. 9 showing the mode clutchand mode shift mechanism in greater detail;

FIG. 12 is an enlarged partial view of FIG. 9 showing components of theintegrated mode and range shift mechanism in greater detail;

FIGS. 13 and 14 are illustrations of an actuator shaft assemblyassociated with the integrated mode and range shift mechanism;

FIGS. 15A through 15F are sectional views generally taken along line A-Aof FIG. 14 showing rotated positions of the mode cam for establishing anumber of different operating modes;

FIG. 16 is a partial sectional view of a two-speed transfer caseconstructed in accordance with a seventh embodiment configured toinclude a range shift mechanism having a range cam;

FIG. 17 is an enlarged partial view showing portions of the range camand the range fork associated with the range shift mechanism of FIG. 16;

FIG. 18 is a perspective view of a range cam and FIG. 18A is an“unrolled” view of the range cam illustrating a guide slot having alow-range dwell segment interconnected to a high-range dwell segment viaa linear (single rate) range shift segment;

FIG. 19 is an unrolled view of a range cam embodying the teachings ofthe present disclosure and including a guide slot having a non-linear,multi-step (multi-rate) range shift segment;

FIG. 20 is an overlay comparison of the multi-step range cam of thepresent disclosure compared to a single-step range cam;

FIG. 21 is a perspective view of a planetary gearset equipped with aconventional carrier unit;

FIG. 22 is a perspective view of the carrier unit shown in FIG. 21illustrating a crack failure due to a stress crack propagating from thespline/clutch teeth to the pinion shaft bore and through the OD of thecarrier unit;

FIG. 23 is a side view of a planetary gearset having a carrier unitconfigured to include a crack arresting feature according to a firstnon-limiting embodiment;

FIG. 24 is an enlarged partial view of the carrier unit shown in FIG. 23for providing additional clarity regarding the crack arresting featureassociated therewith;

FIG. 25 is similar to FIG. 24 but now shows a crack failure propagatedfrom the spline/clutch teeth to the crack arresting feature;

FIGS. 26 and 27 are generally similar to FIGS. 23 and 24, respectively,but illustrate the carrier unit configured to include a crack arrestingfeature according to a second non-limiting embodiment;

FIGS. 28 and 29 are provided to illustrate the carrier unit of theplanetary gearset configured to include a crack arresting featureaccording to a third non-limiting embodiment;

FIGS. 30 and 31 illustrate the carrier unit of the planetary gearsetconfigured to include a crack arresting feature according to a fourthnon-limiting embodiment;

FIG. 32 illustrates the carrier unit of the planetary gearset configuredto include a crack arresting feature according to a fifth non-limitingembodiment, with the crack arresting feature having an arc shape; and

FIG. 33 illustrates a position of the arc-shaped crack arresting featurerelative to a mounting hole of the carrier unit, with the arc-shapedcrack arresting feature disposed in the expected path of a crackpropagating from the teeth of the carrier toward the mounting hole.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings. In particular, a plurality of non-limitingembodiments of a two-speed active transfer case adapted for use withfour-wheel drive vehicles are provided so that this disclosure will bethorough and will fully convey the true and intended scope to those whoare skilled in the art. Numerous specific details are set forth such asexamples of specific components, devices, and methods, to provide athorough understanding of embodiments of the present disclosure. It willbe apparent to those skilled in the art that specific details need notbe employed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “compromises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps operations, elements, components, and/or groups orcombinations thereof. The method steps, processes, and operationsdescribed herein are not to be construed as necessarily requiring theirperformance in the particular order discussed or illustrated, unlessspecifically identified as an order of performance. It is also to beunderstood that additional or alternative steps may be employed.

When an element or layer is referred to as being “on,” “engaged to,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” directly engagedto,” “directly connected to,” or “directly coupled to” another elementor layer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,”“lower,” “above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

Referring initially to FIG. 1 of the drawings, an example drivetrain fora four-wheel drive motor vehicle 10 is shown to include a powertrain 12operable to generate rotary power (i.e., drive torque) which istransmitted through a power transfer unit, hereinafter transfer case 14,to a primary driveline 16 and to a secondary driveline 18. Powertrain 12is shown, in this non-limiting example, to include a power source suchas an internal combustion engine 20 and a transmission 22. In theparticular arrangement shown, primary driveline 16 is a rear drivelineand generally includes a rear axle assembly 24 and a rear propshaft 26arranged to drivingly interconnect a rear output shaft 28 of transfercase 14 to an input of rear axle assembly 24. The input to rear axleassembly 24 includes a hypoid gearset 30 connected to rear propshaft 26.Rear axle assembly 24 includes a rear differential assembly 32 driven byhypoid gearset 30, and a pair of rear axleshafts 34 interconnecting reardifferential assembly 32 to a pair of ground-engaging rear wheels 36.Secondary driveline 18 is a front driveline and includes a front axleassembly 38 and a front propshaft 40 arranged to drivingly interconnecta front output shaft 42 of transfer case 14 to an input of front axleassembly 38. The input to front axle assembly 38 includes a hypoidgearset 44 connected to front propshaft 40. Front axle assembly 38includes a front differential assembly 46 driven by hypoid gearset 44,and a pair of front axleshafts 48 interconnecting front differentialassembly 46 to a pair of ground-engaging front wheels 50.

Motor vehicle 10 is also shown to include a traction control system 54having an electronic controller unit 56 configured to receive inputsignals from vehicle sensors 58 and a mode selector 60 and tosubsequently provide control signals to one or more actuators. Modeselector 60 is, in this non-limiting example, a manually-operable devicewithin the passenger compartment of vehicle 10 and, for example, mayinclude a shift lever. Controller unit 56 can provide control signals toone or more transfer case actuators 62 and an axle disconnect actuator64. As will be detailed with greater specificity, the at least onetransfer case actuators 62 may include a range actuator 62A associatedwith a two-speed range mechanism to provide high-range and low-rangedrive connections, and a mode actuator 62B associated with a modemechanism to provide two-wheel drive and four-wheel drive modes ofoperation.

In some of the embodiments of transfer case 14 to be describedhereinafter, mode selector 60 is adapted to mechanically operate rangeactuator 62A to control operation of the range shift mechanism, asindicated by leadline 65. Range actuator 62A, in such embodiments,provides a range signal to ECU 56 that is indicative of the particulardrive connection (namely, the high-range or the low-range) selected andestablished. Disconnect actuator 64 controls operation of a disconnectdevice 66 associated with front axle assembly 38 for selectivelycoupling and uncoupling front driveline 18 relative to transfer case 14.Sensors 58 are configured to provide information to controller unit 56indicative of the current operational characteristics of vehicle 10and/or road conditions for use in controlling operation of transfer case14. The information provided by sensors 58 may include, withoutlimitations, information related to vehicle speed, driveline/wheelspeeds, acceleration, braking status, steering angle, throttle position,lateral displacement, and/or rain sensors. Mode selector 60 permits avehicle operator to select operation of vehicle 10 in one of theavailable drive modes which may include, without limitation, a two-wheelhigh-range (2WH) drive mode, an automatic four-wheel high-range(AUTO-4WH) drive mode, a locked four-wheel high-range (LOCK-4WH) drivemode, a Neutral mode, a locked four-wheel low-range (LOCK-4WL) drivemode, and an automatic four-wheel low-range (AUTO-4WL) drive mode.

Referring now to FIG. 2 of the drawings, a stick diagram of an exampleembodiment of transfer case 14 constructed in accordance with thepresent disclosure is provided. Transfer case 14 is generally shown toinclude: a housing assembly 70; an input shaft 72 rotatably supported byhousing assembly 70; a two-speed range mechanism 74 disposed betweeninput shaft 72 and rear output shaft 28; a range shift mechanism 76controlling operation of two-speed range mechanism 74; a transfermechanism 78 driven by rear output shaft 28; a mode mechanism 80disposed between transfer mechanism 78 and front output shaft 42; a modeshift mechanism 82 controlling operation of mode mechanism 80; a firstlubrication mechanism 84 associated with rear output shaft 28; and asecond lubrication mechanism 86 (shown in phantom lines) associated withfront output shaft 42. As is evident, range mechanism 74 is arranged inassociation with a first rotary axis “A” of transfer case 14 while modemechanism 80 is arranged in association with a second rotary axis “B” oftransfer case 14. With transfer case 14 installed in vehicle 10, thefirst axis is generally parallel but offset above the second axis withhousing assembly 70 configured to define a sump area 90 filled with alubricating oil in an area generally configured to locate at least aportion of mode mechanism 80 within sump area 90. Transfer case 14 isalso shown in FIG. 2 to include range actuator 62A in association withrange shift mechanism 76, and mode actuator 62B in association with modeshift mechanism 80 which is controlled by controller unit 56.

With particular reference now to FIG. 3, a first non-limiting embodimentof transfer case 14 originally shown in FIGS. 1 and 2, is identified byreference numeral 14A. Housing assembly 70 is shown, in thisnon-limiting example, to include a multi-piece configuration having anadapter housing section 100, a front housing section 102, a rear housingsection 104, and a rear end cap 105. Adapter housing section 100 isconfigured to be rigidly secured to transmission 22 and includes abearing assembly 106 rotatably supporting input shaft 72. Input shaft 72includes internal splines 108 adapted to matingly engage with externalsplines formed on a transmission output shaft. Rear output shaft 28 issupported for rotation relative to input shaft 72 by a first bearingassembly 110 disposed between input shaft 72 and rear output shaft 28,and a second bearing assembly 112 disposed between rear housing section104 and rear output shaft 28.

Range mechanism 74 is shown, in this non-limiting embodiment, to includea planetary gearset 116 and a range clutch 118. Planetary gearset 116includes a sun gear 120 formed integrally on input shaft 72, a ring gear122 non-rotatably fixed to front housing section 102, a carrier unit 124having a plurality of pins 126, and a plurality of planet gears 128 eachrotatably mounted (via a bearing assembly) on a corresponding one ofpins 126 and which are each in constant meshed engagement with sun gear120 and ring gear 122. Input shaft 72 includes a clutch ring segment 130having external clutch teeth 132 formed thereon. Carrier unit 124 can bea two-piece arrangement with a pair of laterally-spaced carrier platesbetween which pins 126 extend or, in the alternative, can be a one-piece(i.e. powdered metal) member formed with openings within which planetgears 128 are rotatably supported on pins 126. Carrier unit 124 may alsoinclude a clutch ring segment 134 having internal clutch teeth 136formed thereon. Range clutch 118 is configured as a sliding range collarthat is splined for common rotation with rear output shaft 28. Rangecollar 118 also includes external clutch teeth 140 and internal clutchteeth 142. Range collar 118 is axially moveable on rear output shaft 28between three (3) distinct range positions.

Range collar 118 is moveable between a high-range (H) position, aneutral (N) position, and a low-range (L) position. When range collar118 is located in its H range position (shifted to the left relative tothe position shown in FIG. 3), its internal clutch teeth 142 engageexternal clutch teeth 132 on input shaft 72 so as to establish a firstor “direct” (i.e., high-range) speed ratio drive connection betweeninput shaft 72 and rear output shaft 28. In contrast, when range collar118 is located in its L range position (illustrated in FIG. 3), itsexternal clutch teeth 140 engage internal clutch teeth 136 on carrierunit 124 so as to establish a second or “reduced” (i.e., low-range)speed ratio drive connection between input shaft 72 and rear outputshaft 28. Location of range collar 118 in its N position disengages rearoutput shaft 28 from driven connection with input shaft 72 and carrierunit 124 so as to interrupt the transfer of drive torque and permitrelative rotation therebetween. Accordingly, the high-range driveconnection is established when range collar 118 is located in its Hrange position and the low-range drive connection is established whenrange collar 118 is located in its L range position. The two-speed rangemechanism shown and described is intended to exemplify any suitable gearreduction device capable of establishing two distinct speed ratio driveconnections between input shaft 72 and rear output shaft 42.

Range shift mechanism 76 is shown, in the non-limiting embodiment, toinclude a shift rail 150 mounted between front and rear housing sections102 and 104 of housing assembly 70, a range fork unit 152 slideablydisposed on shift rail 150, and a rotary-to-linear conversion deviceconfigured as a sector plate 154 having a range guide slot 156 withinwhich a range pin 158 extends. Range pin 158 extends outwardly from atubular hub segment 160 of range fork unit 152 such that rotation ofsector plate 154 causes linear movement of range fork unit 152 due torange pin 158 moving within range guide slot 156. As will be describedwith further detail hereinafter, the profile of the range guide slot 156may comprise a plurality of different cam sections configured tooptimize the axial loading generated to move range collar 118. In apreferred arrangement, a plurality of three (3) interconnected slotsegments of range guide slot 156, each having a different slope (rate),is provided with sector plate 154. Range fork unit 152 further includesa fork segment 162 extending outwardly from hub segment 160 and having apair of bifurcated forks 164 that are retained in an annular groove 166formed in range collar 118. Therefore, axial movement of range fork unit152 results in sliding movement of range collar 118 between its threedistinct range positions. While not specifically shown, a power-operatedversion of range actuator 62A may include an electric motor forrotatably driving a sector shaft 170 that is, in turn, coupled to sectorplate 154 so as to move range fork unit 152 which in turn moves rangecollar 118 into the desired range position in response to rotation ofsector shaft 170. As an alternative, range actuator 62A may include amechanical linkage assembly interconnecting a shift lever in thepassenger compartment of vehicle 10 to sector shaft 170 and which isoperable to cause rotation of sector plate 154 in response to movementof the shift lever. Those skilled in the art will appreciate that anysuitable arrangement capable of axially moving range fork unit 152 tofacilitate movement of range collar 118 between its three (3) distinctrange positions is within the meaning of range actuator 62.

Transfer mechanism 78 is shown in the non-limiting example, to include afirst transfer component driven by rear output shaft 28 and which isarranged to transfer drive torque to a second transfer componentrotatably supported on front output shaft 42. Transfer mechanism 78 is achain and sprocket type of drive assembly including a first sprocket 171acting as the first transfer component, a second sprocket 172 acting asthe second transfer component, and a power chain 174 encircling firstsprocket 171 and second sprocket 172. First sprocket 171 is splined forcommon rotation with rear output shaft 28 and is axially retainedbetween a radial flange 176 and a snap-ring 178. Second sprocket 172 isrotatably mounted on front output shaft 42 via a needle bearing assembly180. A retainer ring 182 and a radial thrust bearing assembly 184 arealso disposed between second sprocket 172 and front output shaft 42.Front output shaft 42 is rotatably supported by housing assembly 70 viaa pair of laterally-spaced roller bearing units 186 and 188. It iscontemplated that alternative transfer mechanisms, such as gear drivearrangements, can be used with transfer case 14A to transfer drivetorque from rear output shaft 28 to a transfer component rotatablysupported on front output shaft 42.

Mode mechanism 80 is best shown in this non-limiting example to includea wet-type multi-plate friction clutch assembly 189 disposed betweensecond sprocket 172 and front output shaft 42 for facilitating adaptivetorque transfer therebetween. Friction clutch assembly 189 generallyincludes a first clutch member or clutch drum 190 fixed for commonrotation with second sprocket 172, a second clutch member or clutch hub192 mounted to, formed integrally with, an intermediate section of frontoutput shaft 42, and a multi-plate clutch pack 193 comprised ofalternatively interleaved outer clutch plates 194 and inner clutchplates 196. Outer clutch plates are splined for rotation with clutchdrum 190 while inner clutch plates are splined for rotation with clutchhub 192. Clutch drum 190 is a formed component and includes a pluralityof oil transfer holes (not shown) configured to permit lubricant to flowtherethrough. A spacer ring 198 is provided between drum 190 and secondsprocket 172.

Friction clutch assembly 189 also includes a spring retainer ring 200fixed (via splines, lugs, etc.) for common rotation with clutch drum190, an axially-moveable apply plate 202 that is connected for commonrotation with spring retainer ring 200, and a plurality ofcircumferentially aligned return springs 204 disposed between springretainer ring 200 and apply plate 202. As will be detailed, returnsprings 204 are configured and arranged to normally bias apply plate 202in a direction toward a retracted position relative to clutch pack 193.Apply plate 202 includes a plurality of axially-extending andcircumferentially-aligned drive lugs 206 which extend through windowapertures 208 formed in spring retainer ring 200. Drive lugs 206 areconfigured to engage and apply a clutch engagement force on clutch pack193, the magnitude of which controls the amount of drive torque that istransferred from clutch drum 190 to clutch hub 192 through clutch pack193. While mode mechanism 80 is shown preferably configured as amulti-plate wet-type friction clutch assembly, those skilled in the artwill recognize that such a mode mechanism is intended to represent anytype of mode clutch or coupling capable of selectively coupling frontoutput shaft 42 for rotation with second sprocket 172 of transfermechanism 78 for facilitating the transfer of drive torque to frontdriveline 18.

Mode shift mechanism 82 is best shown, in the non-limiting example ofFIGS. 3 and 7, to include a motor-driven rotary-to-linear conversiondevice of the type commonly referred to as a ballramp unit. As isevident, FIGS. 3 and 7 illustrate slightly different embodiments of themode shift mechanism 82. The ballramp unit generally includes a firstcam ring 220, a second cam ring 222, and followers 224 disposed inaligned cam tracks formed therebetween. In FIG. 3, the first cam ring220 is shown to the right of the second cam ring 222. In FIG. 7, thefirst cam ring 220 is shown to the left of the second cam ring 222.First cam ring 220 is non-rotatably fixed to housing assembly 70 via ananti-rotation tab. First cam ring 220 is also fixed axially and islocated against a backing plate 228 via a shim ring 230 and a snap ring232. Backing plate 228 is splined for rotation with front output shaft42 such that a radial thrust bearing unit 234 is disposed between firstcam ring 220 and backing plate 228. First cam ring 220 has a pluralityof circumferentially-aligned first cam tracks which followers 224engage. Second cam ring 222 includes a matching plurality of second camtracks against which followers 224 also rollingly engage. A pair of cageplates 238 retain and align followers 224 relative to first cam tracks236 and second cam tracks 240. Second cam ring 222 is adapted to moveaxially relative to first cam ring 220 as a result of rotation of secondcam ring 222 relative to first cam ring 220. As such, the profile and/orcontour of cam tracks and controls the linear motion of second cam ring222. An electric motor 250 acts as mode actuator 62B and has a rotaryoutput driving a gear (not shown) that is meshed with geared racksegment 252 of second cam ring 222.

As will be understood, the direction and amount of rotation of theelectric motor's output controls the direction and amount of rotation ofsecond cam ring 222 which, in turn, controls the direction and amount ofaxial travel of second cam ring 222 relative to the clutch pack. Asshown in FIG. 3, a thrust bearing assembly 254 is disposed between aface surface of second cam ring 222 and a face surface of apply plate202 to accommodate rotation of apply plate 202 relative to second camring 222 during coordinated axial movement of apply plate 202 withsecond cam ring 222. Those skilled in the art will appreciate that thealternative ballramp unit where one or both cam rings are rotatable toestablish axial movement of one of the cam rings is within the scope ofthe ballramp unit disclosed herein. Additionally, other rotary-to-linearconversion devices (i.e., ballscrew units), camming devices or pivotabledevices configured to control the magnitude of the clutch engagementforce applied to clutch pack 193 are considered alternatives for modeshift mechanism 82.

Second cam ring 222 is configured to control axial movement of applyplate 202 between a first or minimum clutch engagement position and asecond or maximum clutch engagement position relative to clutch pack 193of friction clutch assembly 189. With apply plate 202 axially located inits first position, a predetermined minimum clutch engagement force isexerted by drive lugs 206 on clutch pack 193, thereby transferring aminimum amount of drive torque from rear output shaft 28 (throughtransfer mechanism 78) to front output shaft 42. Typically, no drivetorque is transmitted from rear output shaft 28 and transfer mechanism74 through friction clutch assembly 189 when apply plate 202 is locatedin its first position, thereby establishing a “released” mode forfriction clutch assembly 189 and a two-wheel drive mode (2WD) fortransfer case 14A. In contrast, with apply plate 202 axially located inits second position, a predetermined maximum clutch engagement force isexerted by drive lugs 206 on clutch pack 193, thereby transferring amaximum amount of drive torque through friction clutch assembly 189 tofront output shaft 42. In this position, a “fully engaged” mode isestablished for friction clutch assembly 189 and a locked four-wheeldrive mode (LOCK-4WD) is established for transfer case 14A. Precisecontrol over the axial location of apply plate 202 between its first andsecond positions permits adaptive torque transfer from rear output shaft28 to front output shaft 42 so as to establish an on-demand four-wheeldrive (AUTO-4WD) mode for transfer case 14A. Return springs 204 reactbetween spring retainer ring 200 and apply plate 202 so as to normallybias apply plate 202 toward its first position. Those skilled in the artwill recognize that mode shift mechanism 82 can be any suitablepower-operated arrangement operable for controlling movement of applyplate 202 relative to clutch pack 193. While not shown, a power-offbrake can be associated with motor 250 which functions to mechanicallyhold apply plate 202 in its second position to establish the LOCK-4WDmode and allow motor 250 to be turned off when one of the LOCK-4WD modesis selected.

First lubrication mechanism 84 is shown, in this non-limiting example,to include a lube pump 270 having a pump housing 272 non-rotatably fixedto housing assembly 70, and a pump assembly 274 disposed in a pumpchamber formed within housing 272. Pump assembly 274 has a rotary pumpmember fixed for rotation with rear output shaft 28 and which isoperable for drawing lubricant from sump area 90 (through a supply tube276) into a suction-side inlet portion of the pump chamber formed inpump housing 272. Rotation of the rotary pump member caused by rotationof rear output shaft 28 causes the lubricant to be pressurized anddischarged from a pressure-side discharge portion of the pump chamberfor delivery to a central lube channel 278 formed in rear output shaft28 via one or more radial feed ports 280. Thereafter, the lubricant incontrol lube channel 278 is radially dispersed via radial dischargeports to provide lubricant to the various rotary components aligned withthe “A” axis. In one embodiment, lube pump 270 could be a gearotor pump.

Second lubrication mechanism 86 is shown, in this non-limitingembodiment, to be configured to catch lubricant splashed from clutchdrum 190, second sprocket 172 and chain 174 and to transfer the capturedlubricant for use in lubricating and cooling components associated withmode mechanism 80 and other rotary components aligned with the “B” axis.In general, second lubrication mechanism 86 is a “splash recovery”lubrication system that is operable for use in power transfer unitshaving a multi-plate friction clutch assembly disposed, at leastpartially, for rotation in a lubricant sump, such as sump area 90. Thesplash recovery clutch lubrication system associated with the varioustransfer cases of the present disclosure is applicable to other powertransfer units of the type used in vehicular drivetrain applications toprovide a “pumpless” solution to lubricating rotary components alignedfor rotation along a rotary axis positioned in proximity to alubrication sump. The splash recovery clutch lubrication system providesa means for supplying lubricant to a control portion of a rotatingclutch located in the lubricant sump. The present disclosure alsoeliminates pump priming concerns at low RPM since as the rotationalspeed increases, the lubricant splashes and reduces the sump height.However, the recovery system feeds lubricant back into the clutch systemwithout concerns related to conventional pump priming. Other resultingadvantages include minimized spin losses, weight savings, improvedpackaging and noise reduction over conventional pump systems.

Referring now to FIG. 4, an alternative embodiment of transfer case 14is identified by reference numeral 14B. Transfer case 14B issubstantially similar in construction and function to transfer case 14Aof FIG. 3, with the exception that first sprocket 171′ is now drivinglycoupled (i.e., splined) to a drive hub 300 which, in turn, is coupledvia a splined connection 302 to rear output shaft 28′. A pair ofretainer rings 304, 306 axially restrain and locate first sprocket 171′on drive hub 300. Drive hub 300 is retained and axially positionedagainst a radial shoulder 176′ of rear output shaft 28′ via a snap ring308. In addition, clutch hub 192′ is now a separate clutch componentsplined to front output shaft 28. Due to the similarity of the remainingcomponents of transfer case 14B to the previously described componentsassociated with transfer case 14A, common reference numerals are used toidentify similar components and further description is not otherwiserequired. Suffice it to say that transfer case 14B is a two-speed activetransfer case capable of establishing all of the drive modes describedin relations to transfer case 14A.

Referring to FIG. 5, another alternative embodiment of transfer case 14is identified by reference numeral 14C. Transfer case 14C issubstantially similar in construction and functional operation totransfer case 14B of FIG. 4 with the exception that a modified adapterhousing section 101′ is now associated with multi-piece housing 70.Adapter 101′ is secured to housing section 102 via bolts 320 andincludes a plurality of mounting studs 322 arranged for retention inalignment apertures formed in the transmission housing. Input shaft 72extends outwardly from adapter housing 101′. The various arrangementsshown in FIGS. 3 through 5 are provided to illustrate the modularityassociated with the present disclosure.

Referring to FIG. 6, yet another alternative embodiment of transfer case14 is identified by reference numeral 14D. Transfer case 14D isgenerally similar to transfer cases 14A-14C in structure and functionaloperation but is now configured to include a slightly modified rangeshift mechanism 76′ and range mechanism 74′ in combination with amodified housing assembly 70′. Housing assembly 70′ is now shown withadapter section 100 and first housing section 102 of transfer case 14Aintegrated into a common housing section 330. In addition, input shaft72′ is now shown with sun gear 120′ formed on a radially enlarged hubsection and which defines internal sun gear clutch teeth 132′. Externalclutch teeth 140′ on range collar 118′ are now configured to engagecarrier clutch teeth 136′ when range collar 118′ is located in its Lrange position and to engage sun gear clutch teeth 132′ when rangecollar 118′ is located in its H range position. In addition, range shiftmechanism 76′ now includes a range fork 152′ slideably mounted on shiftrail 150′ with its range pin 158′ retained in a range guide slot 165′formed in sector plate 154′. Mode clutch 80 and mode actuator 82 aresimilar to the arrangements previously disclosed. Range guide slot 165′is configured to provide a multi-step (multi-rate) profile foroptimizing the shift forces generated to move range collar 118′.

Referring now to FIG. 8, another alternative embodiment of transfer case14 is identified by reference numeral 14E. Transfer case 14E differsfrom the previously disclosed alternative embodiments of transfer case14 in that it is equipped with an “integrated” power-operated rangeactuator and mode actuator, hereinafter identified as power-operatedshift actuator 62C. Transfer case 14E is generally shown to include: ahousing assembly 350; an input shaft 352 rotatably supported by housingassembly; a rear output shaft 354 rotatably supported by input shaft 352and housing assembly 350; a two-speed range mechanism 356 disposedbetween input shaft 352 and rear output shaft 354; a range shiftmechanism 358 controlling operation of two-speed range mechanism 356; atransfer mechanism 360 driven by rear output shaft 354; a mode mechanism362 disposed between transfer mechanism 360 and a front output shaft364; a mode shift mechanism 366 controlling operation of mode mechanism362; and a splash lubrication system 368, all in addition topower-operated shift actuator 62C. As before, range mechanism 356 isarranged in association with a first rotary axis “A” that is shared withinput shaft 352 and rear output shaft 354 while mode mechanism 362 andfront output shaft share a second rotary axis “B”.

Two-speed range mechanism 356 is generally similar to two-speed rangemechanism 74′ of FIG. 6 and includes planetary gearset 116′ and rangeclutch 118′. Range clutch 118′ is a sliding range collar moveablebetween the H, N, L range positions relative to planetary gearset 116′.Operation of range shift mechanism 358 and mode shift mechanism 366 iscontrolled and coordinated by power-operated shift actuator 62C. Rangeshift mechanism 358 generally includes a rotary shift shaft 370, a rangecam 372 supported for axial movement on shift rail 370, and a range forkunit 374 mounted via a spring-loaded mechanism 376 on a tube segment 378of range cam 372. Range fork unit 374 has a fork section 380 engaging agroove 382 formed in range collar 118′. A range pin 384 is fixed forrotation with shift shaft 370 and extends into a range guide slot 386formed in range cam 372. As will be detailed, range guide slot 386 isconfigured to include a low-range dwell segment and a high-range dwellsegment that are interconnected via a multi-step range shift segment.Shift shaft 370 is shown rotatably supported in housing assembly 350 viaa pair of laterally spaced bearings 388, 390. Spring-loaded mechanism376 is provided to permit axial movement of range cam 372 when a “toothblock” condition exists between range collar 118′ and the clutchingcomponents of planetary gearset 356 to the desired range positionfollowing release of the tooth block condition.

Transfer mechanism 360 is generally similar to transfer mechanism 78 ofFIG. 3 and includes first sprocket 171 formed on rear output shaft 354,a second sprocket 172 rotatably supported on front output shaft 364, andan endless power chain 174 encircled therebetween. Mode mechanism 362 isalso generally similar to mode mechanism 80 shown in FIGS. 4-6 andincludes friction clutch assembly 189 with the components thereofidentified by common reference numbers. Mode shift mechanism 366 is aslightly modified version of the ballramp unit and has a first cam plate394, second cam plate 396, and roller 398 retained in cam tracks formedin the first and second cam plates. First cam plate 394 is supportedagainst a backing ring 228′ extending integrally from front output shaft364 via a bearing assembly 234. Another bearing assembly 254 ispositioned between second cam plate 396 and apply plate 202.

In accordance with the construction shown in FIG. 8, power-operatedshift actuator 62C includes an electric motor 400 having a rotary outputconfigured to drive a reduction gear 402 fixed (i.e., splined) forrotation with shift shaft 370. A mode cam 404, associated with modeshift mechanism 366, is fixed for rotation with shift shaft 370. Modecam 404 includes a first cam surface against which a first followersegment of first cam plate 394 rests, and a second cam surface againstwhich a second follower segment of second cam plate 396 rests. Theconfiguration of the first and second cam surfaces are selected to causeat least one of first cam plate 394 and second cam plate 396 to rotaterelative to the other which, in turn, results in axial movement ofsecond cam plate 396. This axial movement results in corresponding axialmovement of apply plate 202 relative to clutch pack 193, therebyproviding adaptive torque transfer between second sprocket 172 and frontoutput shaft 364. Accordingly, the configuration of range guide slot 386in range cam 372 and the configuration of the mode cam tracks on modecam 404 are selected to facilitate coordinated movement of range forkunit 374 and apply plate 202 to establish each of the available drivemodes. In particular, the low-range dwell segment of range guide slot386 is configured to maintain range collar 118′ in its L range positionwhile the mode cam tracks on mode cam 404 cause movement of apply plate202 to control adaptive actuation of friction clutch assembly 189.Similarly, the high-range dwell segment of range guide slot 386 isconfigured to maintain range collar 118′ in its H range position whilethe mode cam tracks on mode cam 404 cause movement of apply plate 202relative to friction clutch assembly 189. However, the multi-step rangeshift segment of range guide slot 386 is configured to generatenon-linear shift forces required to move range collar 118′ between its Hand L range position, preferably with friction clutch assembly 189 in areleased mode.

Splash lubrication system 368 is shown in FIG. 8 to be configured as a“pumpless” arrangement operable to circulate lubricant splashed duringrotation of second sprocket 172 and chain to lubricate componentsaligned on the rotary axis of front output shaft 364 as well as therotary axis of rear output shaft 354. Lubrication system 368 is shown toinclude a guide housing 410 generally enclosing a portion of power chain174 and first sprocket 171. Guide housing 410 defines a lubricantreservoir segment 412 configured to collect the lubricant. A tube 414fluidically connects reservoir segment 412 to a lube chamber 414 formedwith a bell-shaped lube housing 416 configured to enclose and separateplanetary range mechanism 356. This arrangement is configured to directlubricant to rotary components on mainshaft 352/354.

Referring now to FIGS. 9 through 15, another alternative embodiment oftwo-speed transfer case 14 is identified by reference numeral 14F.Transfer case 14F also is equipped with an integrated power-operatedshift actuator, but is now shown with the multi-plate friction clutchassembly associated with the rear output shaft instead of the frontoutput shaft. Transfer case 14F is generally shown to include: a housing420; an input shaft 422 rotatably supported by housing 420; a rearoutput shaft 424 rotatably supported by input shaft 422 and housing 420;a two-speed range mechanism 426 disposed between input shaft 422 andrear output shaft 424, a range shift mechanism 428 controlling operationof two-speed range mechanism 426; a transfer mechanism 430 driven by afront output shaft 432; a mode mechanism 434 disposed between rearoutput shaft 424 and transfer mechanism 430; a mode shift mechanism 436controlling operation of mode mechanism 434; and a power-operated shiftactuator 438. As before, range mechanism 426 is associated with a firstrotary axis shared with input shaft 422 and rear output shaft 424.However, mode mechanism 434 is now also associated with this first axis.

Two-speed range mechanism 426 is again generally similar to two-speedrange mechanisms 79′ (FIG. 6) and 356 (FIG. 8) and includes a planetarygearset 116′ and a range clutch 118′, as is best shown in FIG. 10.Planetary gearset 116′ includes a sun gear 427 driven by input shaft422, a ring gear 429 non-rotatably fixed to housing 420, and a carrierunit 431 rotatably supporting a plurality of planet gears 433 on pinionposts 435 and which are each in constant mesh with sun gear 427 and ringgear 429. Sun gear 427 is formed to include internal clutch teeth 437while carrier unit 431 is formed to include internal clutch teeth 439.

Range clutch 118′ includes a range collar 440 coupled via a splineconnection for rotation with and axial sliding movement on rear outputshaft 424. Range collar 440 has external clutch teeth 442 adapted toselectively engage either internal clutch teeth 437 formed on inputshaft 422 or internal clutch teeth 439 formed on carrier unit 431. Rangecollar 440 is shown located in a high (H) range position such that itsclutch teeth 442 are engaged with clutch teeth 437 on input shaft 422.As such, a direct speed ratio or “high-range” drive connection isestablished between input shaft 422 and rear output shaft 424. Rangecollar 440 is axially moveable on rear output shaft 424 from its (H)range position through a central neutral (N) range position into a low(L) range position. Location of range collar 440 in its (N) rangeposition functions to disengage its clutch teeth 442 from both inputshaft clutch teeth 437 and carrier clutch teeth 439, thereby uncouplingrear output shaft 424 from driven connection with input shaft 422. Incontrast, movement of range collar 440 into its (L) range positioncauses its clutch teeth 442 to engage clutch teeth 439 on carrier unit431, thereby establishing the reduced speed ratio or “low-range” driveconnection between input shaft 422 and rear output shaft 424.

In the (L) range position, when the input shaft 422 and the sun gear 427rotate together, the sun gear 427 will cause rotation of the meshedplanet gears 433. As the planet gears 433 rotate, the planet gears 433are meshed with the ring gear 429, which is non-rotatably fixed, suchthat the result of the rotation of the planet gears 433 is the rotationof the carrier 439. With the carrier 439 engaged with the clutch teeth442, the rear output shaft 424 thereby rotates in accordance with therotation of the carrier 431.

Referring to FIG. 11, mode mechanism 414 is shown to include a modeclutch 450 having a clutch hub 452 fixed via a spline connection 454 forrotation with rear output shaft 424, a clutch drum 456, and amulti-plate clutch pack 458 operably disposed between clutch hub 452 andclutch drum 456. As seen, clutch pack 458 includes a set of inner clutchplates splined to a cylindrical rim segment 460 of clutch hub 452 andwhich are alternately interleaved with a set of outer clutch platessplined to a cylindrical rim segment 462 of clutch drum 456. Clutch pack458 is retained for limited sliding movement between a reaction platesegment 464 of clutch hub 452 and a pressure plate 466. Pressure plate466 has a face surface 468 adapted to engage and apply a compressiveclutch engagement force on clutch pack 458. Pressure plate 466 issplined to rim segment 460 for common rotation with clutch hub 452 andis further supported for sliding movement on a tubular sleeve segment470 of clutch hub 452. A return spring 472 is provided between clutchhub 452 and pressure plate 466 for normally biasing pressure plate 466away from engagement with clutch pack 458.

Upon engagement of mode clutch 450, drive torque is transmitted fromrear output shaft 424 through clutch pack 458 and transfer mechanism 430to front output shaft 432. Transfer mechanism 430 is a chain drive unitshown to include a first sprocket 480 rotatably supported by bearingassemblies 482 on rear output shaft 434, a second sprocket 484 fixed viaa spline connection 486 to front output shaft 432, and a power chain 488encircling first sprocket 480 and second sprocket 484. Clutch drum 456is fixed for rotation with first sprocket 480 such that drive torquetransferred through mode clutch 450 is transmitted through transfermechanism 430 to front output shaft 432.

Pressure plate 466 is axially moveable relative to clutch pack 458between a first or “fully released” position and a second or “fullyengaged” position. With pressure plate 466 in its fully releasedposition, a minimum clutch engagement force is exerted on clutch pack458 such that virtually no drive torque is transferred through modeclutch 450 so as to establish the two-wheel drive (2WD) mode. Returnspring 472 is arranged to normally urge pressure plate 466 toward itsfully released position. In contrast, location of pressure plate 466 inits fully engaged position causes a maximum clutch engagement force tobe applied to clutch pack 458 such that front output shaft 432 is, ineffect, coupled via transfer mechanism 430 for common rotation with rearoutput shaft 424 so as to establish a locked or “part-time” four-wheeldrive (4WD) mode. Therefore, accurate control of the position ofpressure plate 466 between its fully released and fully engagedpositions permits adaptive regulation of the amount of torque transferbetween rear output shaft 424 and front output shaft 432, therebypermitting establishment of the adaptive or “on-demand” four-wheel drive(AUTO-4WD) mode.

Power-operated shift actuator 438 is operable to coordinate movement ofrange collar 440 between its three distinct range positions withmovement of pressure plate 466 between its fully released and fullyengaged positions. In its most basic form, shift actuator 438 includesan electric motor 500, an actuator shaft 502 driven by electric motor500, range shift mechanism 428, and mode shift mechanism 436. Actuatorshaft 502 has its opposite ends supported by a pair of laterally-spacedbearing assemblies 504 for rotation in housing 420 about a third rotaryaxis. A reduction geartrain 506 provides a drive connection between arotary output of electric motor 500 and actuator shaft 502. Reductiongeartrain 506 includes a worm gearset (not shown) that is driven by therotary output of electric motor 500 and a spur gearset 508. Actuation ofelectric motor 500 causes the worm gearset to drive a drive gear 510associated with gearset 508. Specifically, drive gear 510 is a smalldiameter gear supported for rotation on an idler shaft 511 and which ismeshed with a large diameter driven gear 512 fixed for rotation withactuation shaft 502. In particular, driven gear 512 includes a tubularhub segment 514 that is fixed via a spline connection 516 to actuatorshaft 502 between a radial shaft flange 518 and rear bearing assembly504. The cumulative reduction ratio provided by geartrain 506 permitsthe use of a smaller, low power electric motor. An angular positionsensor or encoder 520 is mounted to an end portion of actuator shaft 502for providing ECU 56 with an input signal indicative of the angularposition of actuator shaft 502.

Range shift mechanism 428 is operable to convert bi-directional rotarymotion of actuator shaft 502 into bi-directional translational movementof range collar 440 between its three distinct range positions.Referring primarily to FIGS. 12 through 14, range shift mechanism 428 isshown to generally include a range cam 524, a range fork 526 and aspring-biasing unit 528. Range cam 524 is a tubular member having aninner diameter surface 530 journalled for sliding movement on actuatorshaft 502. An elongated range guide slot 532 is formed in range cam 524and receives a follower pin 534 that is fixed for rotation with actuatorshaft 502. Guide slot 532 includes a high-range dwell segment 536, alow-range dwell segment 538 and a shift segment 540 interconnectingdwell segments 536 and 538. Range fork 526 includes a sleeve segment 542supported for sliding movement on actuator shaft 502 and a fork segment544 which extends from sleeve segment 542 into an annular groove 546formed in range collar 440. Sleeve segment 542 defines an interiorchamber 548 within which range cam 524 and spring-biasing unit 528 arelocated. Spring-biasing unit 528 is operably disposed between range cam524 and sleeve segment 542 of range fork 526. Spring-biasing unit 528functions to urge range fork 526 to move axially in response to axialmovement of range cam 524 while its spring compliance accommodates tooth“block” conditions that can occur between shift collar clutch teeth 442and input shaft clutch teeth 436 or carrier clutch teeth 438. As such,spring-biasing unit 528 assures that range fork 526 will complete axialmovement of range collar 440 into its H and L range positions uponelimination of any such tooth block condition.

Range shift mechanism 428 is arranged such that axial movement of rangecam 524 relative to actuator shaft 502 results from movement of followerpin 534 within shift segment 540 of range guide slot 532 in response torotation of actuator shaft 502. As noted, such axial movement of rangecam 524 causes range fork 526 to move range collar 440 axially betweenits three distinct range positions. Specifically, when it is desired toshift range clutch 118′ into its high-range drive mode, electric motor500 rotates actuator shaft 502 in a first direction which, in turn,causes concurrent rotation of follower pin 534. Such rotation causesfollower pin 534 to move within shift segment 540 of range guide slot532 for axially moving range cam 524 and range fork 526 until rangecollar 440 is located in its H range position. With range collar 440 inits H range position, the high-range drive connection is establishedbetween input shaft 422 and rear output shaft 424. Continued rotation ofactuator shaft 502 in the first direction causes follower pin 534 toexit shift segment 540 of guide slot 532 and enter high-range dwellsegment 536 for preventing further axial movement of range cam 524,thereby maintaining range collar 440 in its H range position. As will bedetailed, the length of high-range dwell segment 536 of range guide slot532 is selected to permit sufficient additional rotation of actuatorshaft 502 in the first rotary direction to accommodate actuation of modeclutch 450 by mode shift mechanism 436.

With range collar 440 in its H range position, subsequent rotation ofactuator shaft 502 in the opposite or second direction causes followerpin 534 to exit high-range dwell segment 536 and re-enter shift segment540 of range guide slot 532 for causing range cam 524 to begin movingrange collar 440 from its H range position toward its L range position.Upon continued rotation of actuator shaft 502 in the second direction,follower pin 534 exits shift segment 540 of range guide slot 532 andenters low-range dwell segment 538 for locating and maintaining rangecollar 440 in its L range position, whereby the low-range driveconnection between carrier unit 431 and rear output shaft 424 isestablished. Again, the length of low-range dwell segment 538 of rangeguide slot 532 is selected to permit additional rotation of actuatorshaft 502 in the second rotary direction required to accommodatecomplete actuation of mode clutch 450.

Mode shift mechanism 436 is operable to convert bi-directional rotarymotion of actuator shaft 502 into bi-directional translational movementof pressure plate 466 between its fully released and fully engagedpositions so as to permit adaptive regulation of the drive torquetransferred through mode clutch 450 to front output shaft 432. Ingeneral, as shown in FIG. 11, mode clutch actuator assembly 416 includesa ballramp unit 560 and a mode cam 562. Ballramp unit 560 is supportedon rear output shaft 424 between a radial shaft flange 566 and pressureplate 466. Ballramp unit 560 includes a first cam member 568, a secondcam member 570 and balls 572 disposed in aligned sets of tapered grooves574 and 576 formed in corresponding face surfaces of cam members 568 and570. In particular, grooves 574 are formed in a first face surface 578on a cam ring segment 580 of first cam member 568. As seen, a thrustbearing assembly 582 is disposed between shaft flange 566 and a secondface surface 584 of cam ring segment 580. First cam member 568 furtherincludes a tubular sleeve segment 586 and an elongated lever segment588. Sleeve segment 586 is supported on rear output shaft 424 via abearing assembly 590. Lever segment 588 (FIG. 9) has a terminal endportion engaging a spacer collar 592 that is piloted on an and able torotate relative to actuator shaft 502. As shown in FIG. 12, mode cam 562is fixed via a spline connection 563 for common rotation with actuatorshaft 502. A lock ring 596 axially locates spacer collar 592 and modecam 562 relative to a radial shaft flange 598.

Referring again to FIG. 11, second cam member 570 of ballramp unit 560has its grooves 576 formed in a first face surface 600 of a cam ringsegment 602 that is shown to generally surround portions of sleevesegment 586 of first cam member 568 and sleeve segment 470 of clutch hub452. A thrust bearing assembly 604 and thrust ring 606 are disposedbetween a second face surface 608 of cam ring segment 602 and a facesurface 610 of pressure plate 466. Second cam member 570 furtherincludes an elongated lever segment 612 (FIG. 9) having a mode follower614 mounted at its terminal end that rollingly engages a cam surface 616formed on an outer peripheral edge of mode cam 562. As will be detailed,the contour of cam surface 616 on mode cam 562 functions to controlangular movement of second cam member 570 relative to first cam member568 in response to rotation of actuation shaft 502. Such relativeangular movement between cam members 568 and 570 causes balls 572 totravel along tapered grooves 574 and 576 which, in turn, causes axialmovement of second cam member 570. Such axial movement of second cammember 570 functions to cause corresponding axial movement of pressureplate 466 between its fully released and fully engaged positions,thereby controlling the magnitude of the clutch engagement force appliedto clutch pack 450.

Lever segment 612 of second cam member 570 is located on one side ofactuator shaft 502 while lever segment 588 of first cam member 568 islocated on the opposite side of actuator shaft 502. Due to engagement ofmode follower 614 with cam surface 616 on mode cam 562, second cammember 570 is angularly moveable relative to first cam member 568between a first or “retracted” position and a second or “extended”position in response to rotation of actuator shaft 502. With second cammember 570 rotated to its retracted position, return spring 472 biasespressure plate 466 to its fully released position which, in turn, urgesballs 572 to be located in deep end portions of aligned grooves 574 and576. Thus, such movement of second cam member 570 to its angularlyretracted position relative to first cam member 568 also functions tolocate second cam member 570 in an axially retracted position relativeto clutch pack 456. While not shown, a biasing unit may be providedbetween the lever segments to assist return spring 472 in normallyurging second cam member 570 toward its retracted position. In contrast,angular movement of second cam member 570 to its extended positioncauses balls 572 to be located in shallow end portions of alignedgrooves 574 and 576 which causes axial movement of second cam member 570to an axially extended position relative to clutch pack 456. Such axialmovement of second cam member 570 causes pressure plate 466 to be movedto its fully engaged position in opposition to the biasing exertedthereon by return spring 472. Accordingly, control of angular movementof second cam member 570 between its retracted and extended positionsfunctions to control concurrent movement of pressure plate 466 betweenits fully released and fully engaged positions.

As previously noted, cam surface 616 of mode cam 562 and range guideslot 532 of range cam 524 are configured to coordinate movement of rangecollar 440 and pressure plate 466 in response to rotation of actuatorshaft 502 for establishing a plurality of different drive modes.According to one possible arrangement, mode selector 60 could permit thevehicle operator to select from a number of different two-wheel andfour-wheel drive modes including, for example, the two-wheel high-rangedrive (2WH) mode, the on-demand four-wheel high-range drive (AUTO-4H)mode, the part-time four-wheel high-range drive (4HI) mode, the Neutral(N) mode and the part-time four-wheel low-range drive (4LO) mode.Specifically, control system 54 functions to control the rotatedposition of actuator shaft 502 in response to the mode signal deliveredto ECU 56 by mode selector 60 and the sensor input signals sent bysensors 58 to ECU 56.

FIG. 15A illustrates actuator shaft 502 rotated to a “2H” positionrequired to establish the two-wheel high-range drive (2WH) mode. Asunderstood, the two-wheel high-range drive mode is established whenrange collar 440 is located in its (H) range position and pressure plate466 is located in its fully released position relative to clutch pack456. As such, input shaft 422 drives rear output shaft 424 at a directspeed ratio while mode clutch 450 is released such that all drive torqueis delivered to rear driveline 16. Mode follower 614 is shown engaging adetent portion of a first cam segment 616A of cam surface 616 on modecam 562 which functions to locate second cam member 570 in its retractedposition.

If the on-demand four-wheel high-range drive (AUTO-4H) mode isthereafter selected, electric motor 500 is energized to initially rotateactuator shaft 502 in a first (i.e., clockwise) direction from its 2Hposition to an “ADAPT-H” position shown in FIG. 15B. In this rotatedposition of actuator shaft 502, follower pin 534 is located withinhigh-range dwell segment 536 of range guide slot 532 in range cam 524such that range collar 440 is maintained in its (H) range position formaintaining the direct drive connection between input shaft 422 and rearoutput shaft 424. However, such rotation of actuator shaft 502 to itsADAPT-H position causes concurrent rotation of mode cam 562 to theposition shown which, in turn, causes mode follower 614 to engage afirst end portion of a second cam segment 616B of mode cam surface 616.Such movement of mode follower 614 from first cam segment 616A to secondcam segment 616B causes second cam member 570 to move angularly relativeto first cam member 568 from its retracted position to an intermediateor “ready” position. With second cam member 570 rotated to its readyposition, ballramp unit 560 causes pressure plate 466 to move axiallyfrom its fully released position into an “adapt” position that isoperable to apply a predetermined “preload” clutch engagement force onclutch pack 458. The adapt position of pressure plate 466 provides a lowlevel of torque transfer across mode clutch 450 that is required totake-up clearances in clutch pack 458 in preparation for adaptive torquecontrol. Thereafter, ECU 56 determines when and how much drive torqueneeds to be transmitted across mode clutch 450 to limit driveline slipand improve traction based on the current tractive conditions andoperating characteristics detected by sensors 58. As an alternative, theadapt position for pressure plate 466 can be selected to partiallyengage mode clutch 450 for establishing a desired front/rear torquedistribution ratio (i.e., 10/90, 25/75, 40/60, etc.) between frontoutput shaft 432 and rear output shaft 424.

The limits of adaptive control in the on-demand four-wheel high-rangedrive mode are established by controlling bi-directional rotation ofactuator shaft 502 between its ADAPT-H position of FIG. 15B and its“LOCK-H” position shown in FIG. 15C. With actuator shaft 502 in itsLOCK-H position, second segment 616B of mode cam surface 616 causessecond cam member 570 to move to its extended position, thereby causingpressure plate 466 to move to its fully engaged position for fullyengaging mode clutch 450. This range of angular travel of actuator shaft502 causes follower pin 534 to travel within high-range dwell segment536 of range guide slot 532 so as to maintain range collar 440 in its(H) range position. However, such rotation of actuator shaft 502 resultsin mode follower 614 riding along second segment 616B of cam surface 616which, in turn, is configured to control angular movement of second cammember 570 between its ready position and its extended position.Bi-directional rotation of actuator shaft 502 within this range oftravel is controlled by ECU 56 actuating electric motor 500 based on apre-selected torque control strategy. As will be understood, any controlstrategy known in the art for adaptively controlling torque transferacross mode clutch 450 can be utilized with the present invention.

If the vehicle operator selects the part-time four-wheel high-rangedrive (4HI) mode, electric motor 500 is energized to rotate actuatorshaft 502 in the first direction to its LOCK-H position shown in FIG.15C. As such, range collar 440 is maintained in its (H) range positionand mode cam 614 causes second cam member 570 to move to its extendedposition which, in turn, moves pressure plate 466 to its fully engagedposition for fully engaging mode clutch 450. To limit the on-timeservice requirements of electric motor 500, a power-off brake 640associated with electric motor 500 can be engaged to brake rotation ofthe motor output so as to prevent back-driving of geartrain 506 and forholding pressure plate 466 in its fully engaged position. In thismanner, electric motor 500 can be shut-off after the part-timefour-wheel high-range drive mode has been established.

If the Neutral mode is selected, electric motor 500 is energized torotate actuator shaft 502 in a second (i.e., counterclockwise) directionto the Neutral position shown in FIG. 15D. Such rotation of actuatorshaft 502 causes follower pin 534 to exit high-range dwell segment 536and ride within shift segment 540 of range guide slot 532 until rangecollar 440 is located in its (N) position. Concurrently, rotation ofmode cam 562 causes mode follower 614 to engage a portion of firstsegment 616A of cam surface 616 that is configured to move second cammember 570 to a position displaced from its retracted position. Suchmovement of second cam member 570 results in limited axial movement ofpressure plate 466 from its fully released position toward clutch pack456. Preferably, such movement of pressure plate 466 does not result inany drive torque being transferred through mode clutch 450 to frontdriveline 18.

FIGS. 15E and 15F illustrate continued rotation of actuator shaft 502 inthe second direction which occurs when the part-time four-wheellow-range drive (4LO) mode is selected. In particular, FIG. 15E shows anintermediate “ADAPT-L” position of actuator shaft 502 whereat range pin534 enters low-range dwell segment 538 of range guide slot 532 forlocating range collar 440 in its (L) range position. Mode cam 562 haslikewise been rotated for locating mode follower 614 at the interfacebetween first segment 616A of cam surface 616 and a third segment 616Cthereof. The contour of third segment 616C is configured such thatsecond cam member 570 will be rotated to its ready position when modefollower 614 is in the position shown. As previously noted, movement ofsecond cam member 570 to its ready position causes pressure plate 466 tomove axially to its adapt position. However, selection of the part-timefour-wheel low-range drive mode causes continued rotation of actuatorshaft 502 to its LOCK-L position shown in FIG. 15F. Low-range dwellsegment 538 in range guide slot 532 maintains range collar 440 in its Lrange position while third segment 616C of mode cam surface 616 causesmode follower 614 to move second cam member 570 to its extendedposition, thereby moving pressure plate 466 to its fully engagedposition for fully engaging mode clutch 450. Again, power-off brake 640can be actuated to maintain actuator shaft 502 in its LOCK-L position.

Based on the specific arrangement disclosed for power-operated shiftactuator unit 418, actuator shaft 502 is rotatable through a first rangeof angular travel to accommodate range shifting of range collar 440 aswell as second and third ranges of angular travel to accommodateengagement of mode clutch 450. In particular, the first range of angulartravel for actuator shaft 502 is established between its ADAPT-H andADAPT-L positions. The second range of travel for actuator shaft 502 isdefined between its ADAPT-H and LOCK-H positions to permit adaptivecontrol of mode clutch 450 with range collar 440 in the (H) rangeposition. Likewise, the third range of actuator shaft travel is definedbetween its ADAPT-L and LOCK-L positions to permit actuation of modeclutch 450 while range collar 440 is in its (L) range position. In theconstruction shown, power-operated clutch actuation unit 438 utilizes asingle powered device (i.e., electric motor 500) to control actuation ofboth range shift mechanism 408 and mode shift mechanism 416.

As previously noted, sector plates 154 (FIG. 4), 154′ (FIG. 6), rangecam 372 (FIG. 8) and range cam 524 (FIG. 9) are each operable as a“rotary-to-linear” conversion device configured to convert input torquefrom the power-operated shift actuator into an axially-directed shiftforce used to axially move the range clutch between its distinct rangepositions. In each instance, this conversion device included a rangeguide slot configured to have a first (high-range) dwell segment and asecond (low-range) dwell segment interconnected via a third (rangeshift) segment. In conventional two-speed transfer case range shiftarrangements, the range shift segment of the range guide slot associatedwith the conversion device has a linear, single-rate camming profile.One example of this arrangement is shown in FIGS. 18 and 18A in which asingle rate (“single step”) range cam “RC” includes a range guide slot“GS” adapted to retain the range pin therein. The range guide slot (GS)is configured to include a high-range dwell (“HRD”) segment, a low-rangedwell (“LRD”) segment, and an intermediate range shift (“RS”) segment.With respect to 360° of angular travel, this range cam (RC) is shown inthis non-limiting embodiment, with the high-range dwell (HRD) segmentextending 170°, the range shift (RS) segment extending 70°, and thelow-range dwell (LRD) segment extending 110°. In this arrangement, 70°of rotation of the range cam (RC) is used for moving the range clutchbetween its high-range and low-range positions. As can be seen best inFIG. 18A, range shift segment (RS) has one continuous camming(single-rate) profile, identified by angle “A”. Range cam (RC) shown inFIG. 18 is shown with internal splines for common rotation with actuatorshaft 502 associated with transfer case 14F of FIGS. 16 and 17. However,a non-splined version of range cam (RC) could be used in associationwith any of the previously disclosed transfer cases 14E (FIG. 8) and 14F(FIG. 9).

In contrast to this arrangement, the rotary-to-linear conversion devicesof the present disclosure may be configured to include a range guideslot having a range shift segment defining a multi-step (multi-rate)camming profile for generating optimized axially-directed shift forces.Accordingly, a non-limiting embodiment of a range cam 700 is shown inFIG. 19 to be a modified version of range cam (RC) of FIGS. 18 and 18A.Specifically, range cam 700 is formed to include a range guide slot 702having a high-range dwell segment 704, a low-range dwell segment 706,and a multi-step range shift segment 708. Multi-step range shift segment708 of range guide slot 702 is shown to include a plurality of distinctcamming profiles which, in this non-limiting version, are comprised of afirst (high-range) cam portion 710, a second (low-range) cam portion712, and a third (central) cam portion 714 interconnecting first camportion 710 and second cam portion 712. It should be noted that thesethree (3) distinct cam portions are still provided within the 70° rangeshift segment 708 while range guide slot 702 also still includes a 170°high-range dwell segment 704 and a 110° low-range dwell segment 706. Assuch, range cam 700 can be directly substituted for range cam (RC)without tear up of an otherwise conventional range shift system and yetfunctions to generate more axial force without increasing the rotationalinput torque requirements. Further, this multi-step configuration isconfigured to increase the shift forces only at times during the rangeshift operation in which greater shift forces are required and todecrease the shift forces at those times during the range shiftoperation in which less shift forces are required.

With continued reference to FIG. 19, range shift segment 708 of guideslot 702 is shown with first cam portion 710 defining a first angle “B”,second cam portion 712 defining a second angle “C”, and third camportion 714 defining a third angle “D”. FIG. 20 illustrates a layovercomparison of shift segment 708 of range cam 700 to the range shiftsegment of range cam (RC). As seen, high-range cam portion 710 extends20.8°, low-range cam portion 712 extends 11.1° and central cam portion714 extends 38.1° to define the total 70° of angular travel associatedwith multi-step range shift segment 708. Also to be recognized is thatangles B and C are greater than angle A (FIG. 18A), while angle D isless than angle A. Thus, three distinct camming portions or “shiftphases” are established when range cam 700 is rotated to move the rangeclutch between its high-range and low-range positions. As understood,range cam 700 can be axially moveable when used in associations withtransfer cases 14E (FIG. 8) and 14F (FIG. 9) in response to engagementof follower 384, 534 within the range guide slot due to rotation ofactuator shaft. Alternatively, range cam 700 can be fixed for rotationwith actuator shaft (FIGS. 16-17).

FIGS. 16 and 17 illustrate another non-limiting arrangement of a rangemechanism 426 and a range shift mechanism 428 adapted for use with anyof the two-speed transfer case previously disclosed, and particularlytransfer case 14F of FIGS. 9 through 12. In this arrangement, range cam700 is fixed for rotation with actuator shaft 502. Actuator shaft 502 isshown surrounding and rotatably supported on shift rail 150. A two-piecerange fork unit 720 includes range fork 722 and a slider bracket 724.Range fork 722 includes a cylindrical hub segment 726 and a fork segment728 coupled to range collar 440. A spring-load mechanism 730 is disposedbetween slider bracket 724 and hub segment 726 of range fork 722. Sliderbracket 724 includes an extension 732 having a range pin 734 located toextend into range guide slot 702 of range cam 700. Upon rotation ofactuator shaft 502, range cam 700 is currently driven such thatlocations of range pin 734 within guide slot 702 functions to controlaxial movement of range fork unit 720 relative to shift rail 150 forcontrolling movement of range collar 440 between its three distinctrange positions with respect to planetary gearset 116′. As previouslynoted, range shift segment 708 of guide slot 702 is configured in amulti-step arrangement for varying the shift force applied to rangecollar 440 when shifting between its (L) range and (H) range positions.

In each of the transfer case embodiments disclosed herein, the two-speedrange mechanism included a planetary gearset comprised of a sun gear, aring gear, a carrier unit, and a plurality of planet gears rotatablysupported by the carrier unit and in constant mesh with the sun and ringgears. Obviously, other versions/types of planetary gearset arrangementscan be used without deviating from the following discussion relating tointegration of a “crack arresting” feature into the carrier unit. Inthis regard, FIG. 21 illustrates a planet carrier assembly 800 having acarrier unit 802 and planet gears 804 rotatably supported on pinionposts 806. As previously disclosed, planet gears 804 would be inconstant meshed engagement with a sun gear and a ring gear to causecarrier unit 802 to be driven at a reduced speed relative to the sungear.

Thus, when the carrier unit 802 is engaged with the output shaft todrive the output shaft, the output shaft will rotate at a reduced speedrelative to the input shaft and the sun gear.

Carrier unit 802 is shown, in this non-limiting arrangement, to includea carrier ring 810 and a carrier hub 812. Carrier ring 810 is formed toinclude a plurality of equidistant and circumferentially-aligned postholes 814 through which the end of pinion posts 806 extend. Indentations816 extend from post holes 814 to permit the end of each pinion post 806to be swaged or otherwise deformed to secure posts 806 to carrier ring810.

Disposed between each post hole 814, carrier ring 810 also includesmounting holes 818 which are configured to align with similar mountingholes (not shown) formed in axially-extend web segments 820 of carrierhub 812. Web segments 820 extend from a plate segment 822 of carrier hub812. Mounting pins 824 are press-fit into the aligned mounting holes 818to rigidly secure carrier ring 810 to web segments 822 of carrier hub812.

Obviously, alternative methods can be used to rigidly fix carrier ring810 and carrier hub 812 together. Additionally, as described above, thecarrier 802 may also be formed in other ways in which a pair of platesare spaced apart and which support the posts 806 on which planet gears804 may rotate. In another aspect, the structure of the carrier 802 thatsupports the posts may be formed as a one-piece member, such as viasintering or the like. For the purposes of discussion, the carrier 802will be discussed as illustrated, in which the carrier ring 810 issecured to the carrier hub 812.

Windows 826 are formed between adjacent web segment 822 and betweencarrier ring 810 and plate segment 822. Planet gears 804 are locatedwithin windows 826. Carrier ring 810 also includes clutch teeth 830. Asshown, clutch teeth 822 are in the form of internal teeth. As previouslynoted, clutch teeth 830 on carrier unit 802 are provided to selectivelyengage external clutch teeth on the range collar when the four-wheellow-range drive mode is established. When the external clutch teeth ofthe range collar engage with the clutch teeth 830 of the carrier 802,the rotation and torque of the carrier 802 will drive the output shaft.When the clutch teeth 830 of the carrier 802 are not engaged with theexternal clutch teeth of the range collar, the carrier 802 may stillrotate in accordance with the rotation of the sun gear and planet gears,but the rotation of the carrier 802 will not be transferred to theoutput shaft, which will instead operate in neutral or be rotated alongwith the input shaft, depending on the position of the range collar, asdescribed above.

FIG. 22 illustrates a crack failure of carrier unit 802 due to a crack840 which originated at one of clutch teeth 830 and propagated throughmounting hole 814 to the OD of carrier ring 810. Such a crack 840 mayresult from fatigue stress generated during low-range operation when themost stress is placed on carrier unit 802. The added stress during thislow-range operation may result from the carrier unit 802 being used todrive the output shaft and reaction forces imparted on the teeth 830.

As shown, crack 840 has a first portion “C¹” extending from one ofclutch teeth 830 to mounting hole 814 and a second portion “C²”extending from mounting hole 814 to a peripheral edge surface 832 ofcarrier ring 810.

To address and overcome such crack failure incidents, the presentdisclosure is directed to integrating a “crack arresting” feature intocarrier ring 810 of carrier unit 802. Thus, while a crack may be stillproduced on the carrier unit 802, such as a crack propagating from theteeth 830, such a crack may be limited in the degree to which it canpropagate toward the mounting hole 814 and/or the outer peripheral edge832.

FIGS. 23-25 illustrate carrier ring 810 modified to include a pluralityof crack mitigating apertures 850 in general proximity to clutch teeth830 and which provide a first non-limiting embodiment of the crackarresting feature. In particular, apertures 850 may be through and/orpartial depth holes or bores 852 (hereinafter referred to as bores 852,but it will be appreciated that reference to the bores 852 may refer toboth through and partial depth holes/bores) positioned at a diameterfrom the center of carrier ring 810 and are located between clutch teeth830 and pinion post holes 814. The diameter from the center of thecarrier ring 810 on which the bores 852 are disposed is a diameter thatis greater than the diameter of the clutch teeth 830 and less that thediameter on which the mounting holes 814 are centered.

As shown, crack mitigating bores 852 are circumferentially-aligned alonga common diameter and are equally-spaced apart. In another aspect, thebores 852 may be spaced apart in an unequal fashion, with the spacebetween a pair of adjacent bores 852 being smaller or larger than thespacing from the next circumferentially adjacent bore 852. The number ofbores 852, their size and depth, and their spacing can be selected tobest address each specific application and use environment for providingoptimized crack mitigation.

As shown in FIG. 23, there are a greater number of bores 852 (sixteen)than there are mounting holes 814 (six). The bores 852 are also shown asbeing smaller in individual diameter than the diameter of the mountingholes. However, it will be appreciated that the number of bores 852 maybe the same or less than the number of mounting holes 814, depending onthe overall size and shape of the carrier unit 802, the size and numberof posts 806 and planet gears 804, etc. The size of the bores 852 mayalso be the same as or greater than the size of the mounting holes 814or posts 806.

The inclusion of the bores 852 provides for a crack-arresting feature ofthe carrier unit 802. FIG. 25 illustrates a crack “C³” extending fromone of clutch teeth 830 and terminating at one of crack mitigating bores852, but not propagating any further in a radial outward direction.Thus, the strength and rigidity of carrier unit 802 will not be furtherreduced, thereby allowing continued operation of transfer case 14 andextending its service life. It should be understood that crackmitigating bores 852 can be oriented to be aligned with either of pinionpost holes 814 and/or mounting holes 818 or, in the alternative,configured in a staggered orientation therebetween.

Referring now to FIGS. 26 and 27, an alternative configuration of thecrack arresting feature is shown integrated into carrier ring 810 ofcarrier unit 802. In this regard, carrier ring 810 is shown to nowinclude a first plurality of crack mitigating apertures 850A and asecond plurality of crack mitigating apertures 850B which togetherdefine a second non-limiting embodiment of the crack arresting feature.

The first plurality of apertures 850A include a series of through and/orpartial depth holes or bores 852A positioned at a first diameter fromthe center of carrier ring 810 while the second plurality of apertures850B include a series of through and/or partial depth holes or bores852B positioned at a second diameter from the center of carrier ring810. As described previously, further reference to the bores 852A, 852Bwill be understood to encompass both partial depth bores andthrough-holes. The number and dimensions (i.e. diameter, depth, etc.) offirst diameter bores 852A may be identical to or different from thenumber and dimensions of second diameter bores 852B based ondetermination of an optimized configuration to prevent propagation of astress crack from clutch teeth 830 beyond first diameter bores 852A.

The first plurality of bores 852A may be centered on a diameter from thecenter of the carrier ring 810 that is greater than the diameter onwhich the second plurality of bores 852B are centered. Thus, in adirection from the center of the carrier ring 810 moving radiallyoutward, the teeth 830 are followed by the second plurality of bores852B, which are followed by the first plurality of bores 852A, which arefollowed by the mounting holes 814.

The first plurality of bores 852A may be evenly circumferentially spacedalong the diameter on which they are centered. Alternatively, the firstplurality of bores 852A may be un-evenly circumferentially spaced. Thesecond plurality of bores 852B may likewise be evenly or unevenly spacedcircumferentially along the diameter on which they are centered.

In one aspect, the first plurality of bores 852A and second plurality ofbores 852B may be circumferentially staggered, such that each of thefirst plurality of bores 852A is disposed circumferentially betweenadjacent ones of the second plurality of bores 852B, when there are thesame number of bores 852A and 852B. When there are a different number,some of the bores 852A may be circumferentially between some of thebores 852B, and others may be aligned. When circumferentially staggered,the circumferential spacing may be even between adjacent ones of theopposite set of bores 852A or 852B. Alternatively, staggering may beuneven relative to adjacent ones of the opposite set of bores, such thatthe distance to an adjacent bore in one direction is less than thedistance to the adjacent bore in the opposite direction.

In yet another aspect, the bores 852A and 852B may be non-staggered, andinstead be aligned in the same radial direction, such that they are notcircumferentially offset or staggered. In this arrangement, the pairs ofbores 852A and 852B bay be aligned with or offset from the mountingholes 814.

Referring now to FIGS. 28 and 29, another alternative configuration ofthe crack arresting feature is shown integrated into carrier ring 810 ofcarrier unit 802. In this regard, a carrier ring 810 is now shownmodified to include a plurality of crack mitigating apertures 850C whichprovide a third non-limiting embodiment of the crack arresting feature.In particular, apertures 850C are configured as a plurality ofcircumferentially-aligned and equidistantly-spaced lobe-type holes orbores 852C, of through and/or partial depth, each comprising a firstbore portion 854 intersecting with a second bore portion 856. Lobe-typebores 852C are shown aligned along a common diameter, but a staggeredarrangement is also contemplated as being an alternative configuration.While the dimensions (i.e. size and depth) of first portion 854 andsecond portion 856 of lobe-type bores 852C are shown to be generallyidentical, it is understood that variations in such dimensions betweensuch first and second portions of lobe-type bores 852C is likewisecontemplated within the scope of this disclosure.

Similar to the above description of the bores 852, the circumferentialspacing may also be uneven. The various alternative spacing and sizesdescribed above with respect to the bores 852 may also be applied to thebores 852C.

FIGS. 30 and 31 illustrate a fourth alternative embodiment of the crackarresting feature associated with carrier ring 810 of carrier unit 802.In particular, a first plurality of lobe-type crack mitigating apertures850D and a second plurality of lobe-type crack mitigation apertures 850Eare shown aligned in a staggered orientation along first and seconddiameters relative to clutch teeth 830. The first plurality of lobe-typeapertures 850D include a series of through and/or partial depth holes orbores 852D each having a first bore portion 854D and a second boreportion 856D. The dimensions (i.e. diameter and depth) of first andsecond bore portions 854D, 856D may be identical or different. Thesecond plurality of lobe-type crack mitigating apertures 850E include aseries of through and/or partial depth holes or bores 852E, each havinga first bore portion 854E and a second bore portion 856E. The dimensions(i.e. diameter and depth) of first and second bore portions 854E, 856Emay be identical or different. FIG. 31 illustrates the overall size offirst apertures 850D to be generally smaller than the overall size ofsecond apertures 850E to reflect one non-limiting arrangement.

The above described alternative spacing described with respect to thebores 852A and 852B may also be applied to the apertures 850D and 850E.

FIGS. 32 and 33 illustrate a fifth alternative embodiment of the crackarresting feature associated with carrier ring 810 of carrier unit 802.In particular, a plurality of arc-shaped apertures 860 may be disposedon the carrier ring 810. The apertures 860 may have a first end 860A anda second end 860B, with the first end 850A being closer to the center ofthe carrier ring 810. The apertures may extend fully through the carrierring 810, or may be partial depth apertures that extend into the surfaceof the carrier ring 810 but do not extend fully through the carrier ring810.

The apertures 860 may be positioned by utilizing finite element analysis(FEA) to define the specific shape and location of the crack arrestingfeature. With reference to FIG. 32, torque may applied in the clockwisedirection when the carrier ring 810 is highest loaded, as shown by thearrow. As described above, the feature may be a crescent or arc-shapedaperture 860. Based on the FEA, the aperture 860 may be disposed betweenthe mounting holes 814 and the clutch teeth 830 and in the area wherecompressive stress is present due to the clockwise torque illustrate inFIG. 32.

Similar to the above-described crack-arresting features, the aperture860 is positioned and shaped to intercept a crack, such as crack C4 inFIG. 32, that propagates from the teeth 830 toward the mounting hole814. In this manner, the aperture 860 may be positioned to block themounting hole 814 from receiving the crack C4 as it propagates.

With reference to FIG. 33, the mounting hole 814 is shown centeredbetween four quadrants I-IV. The aperture is disposed in quadrant IV,which is the quadrant in which the crack C4 will propagate when thetorque is clockwise.

In one aspect, the inner portion of the aperture 860 may be alignedapproximately parallel to the load path as it approaches the clutchteeth 830. The aperture 860 may then also follow the contour of themounting hole 814 to define its arcuate shape and develop the outer edgeof the arc-shape. The actual radius and/or width of the aperture may bedetermined and refined based on FEA and actual stress patterns.

In this approach, with the arc-shaped apertures 860 operating to blockthe mounting holes 814 from receiving a propagating crack, there may bean equal number of apertures 860 as there are mounting holes 814, withone aperture 860 associated with each one of the mounting holes 814. Theapertures 860 may be centered on a common diameter relative to thecenter of the carrier ring 810, such that apertures 860 areapproximately the same distance from each of the mounting holes 814.

In another aspect, the apertures 860 may be centered on differentdiameters from the center of the carrier ring 810, being shifting in thedirection of the expected crack propagation toward the mounting hole 814to which the aperture 860 is associated, such that some apertures 860may be closer to the teeth 830 than others.

In another aspect, the number of apertures 860 may be doubled relativeto the mounting holes 814, and the additional apertures 860 may besimilarly positioned to receive a crack propagating from the oppositedirection to account for torques that are created in both the clockwiseand counter-clockwise direction.

The apertures 860 may all be the same size, or they may have differentsizes, depending on the FEA.

The present disclosure is not limited to carrier units of the type usedonly in two-speed planetary gearsets in transfer cases or other types ofpower transfer assemblies (i.e. automatic transmissions, etc.), but canbe used with any carrier unit of any planetary gearset exposed tocyclical loading and fatigue stress. While carrier unit 802 is disclosedas a two-piece unit, single-piece configurations are also within thescope of this disclosure. While not limited thereto, powered metalcarrier units can be formed with the crack arresting apertures withoutthe need of a secondary machining operation.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

What is claimed is:
 1. A planetary gearset comprising: a sun gear; aring gear; a carrier unit; a planet gear rotatably supported by saidcarrier unit and in meshed engagement with said sun gear and said ringgear, wherein said carrier unit is formed to include at least one crackarresting feature configured to inhibit propagation of a stress crack.2. The planetary gearset of claim 1, wherein the carrier unit includesclutch teeth adapted to be selectively engaged with a clutch, whereinsaid at least one crack arresting feature is located in proximity tosaid clutch teeth to inhibit propagation of the stress crack originatingat one of said clutch teeth.
 3. The planetary gearset of claim 2,wherein said crack arresting feature includes a plurality of crackmitigating apertures formed in said carrier unit adjacent to said clutchteeth.
 4. The planetary gearset of claim 3, wherein said apertures arealigned along a common diameter and are circumferentially-oriented withrespect to said clutch teeth.
 5. The planetary gearset of claim 4,wherein said apertures are throughbores.
 6. The planetary gearset ofclaim 4, wherein said apertures are partial depth bores.
 7. Theplanetary gearset of claim 4, wherein said apertures are lobe-shaped. 8.The planetary gearset of claim 4, wherein said apertures are arc-shaped.9. The planter gearset of claim 8, wherein said apertures include aradially inner end and a radially outer end and define a curvaturetherebetween.
 10. The planetary gearset of claim 2, wherein said crackarresting feature includes a plurality of first crack mitigatingapertures and a plurality of second crack mitigating apertures, whereinsaid first and second apertures are formed in said carrier unit adjacentto said teeth, and wherein said first apertures are aligned along afirst diameter and said second apertures are aligned along a seconddiameter.
 11. The planetary gearset of claim 10, wherein said firstapertures are staggered with respect to said second apertures.
 12. Theplanetary gearset of claim 3, wherein said carrier unit is a powderedmetal component, and wherein said crack arresting feature is a crackmitigating aperture formed in the carrier unit during powdered metalfabrication.
 13. The planetary gearset of claim 1, wherein said carrierunit includes a central aperture, and wherein said crack arrestingfeature is oriented in proximity to said central aperture, wherein saidfeature includes a plurality of crack mitigating bores surrounding saidcentral aperture.
 14. A transfer case for a vehicle, the transfer casecomprising: a rotary input shaft operational at a first speed; a rotaryoutput shaft; a sun gear configured for concurrent rotation with therotary input shaft; a ring gear; a carrier unit; a planet gear rotatablysupported by said carrier unit and in meshed engagement with said sungear and said ring gear; a range mechanism configured to shift betweenmeshed engagement with the rotary input shaft to drive the rotary outputshaft at the first speed and meshed engagement with the carrier unit todrive the rotary output shaft at a second speed; wherein said carrierunit is formed to include at least one crack arresting featureconfigured to inhibit propagation of a stress crack.
 15. The transfercase of claim 14, wherein the crack arresting feature comprises aplurality of apertures extending at least partially through a carrierring of the carrier unit, wherein the carrier ring includes a pluralityof teeth configured for meshed engagement with the range mechanism and aplurality of mounting holes for supporting the planet gears forrotation, wherein the plurality of apertures are disposed radiallybetween the plurality of teeth and the mounting holes.
 16. The transfercase of claim 15, wherein all of the plurality of apertures are arrangedat approximately the same diameter from a diametrical center of thecarrier unit.
 17. The transfer case of claim 15, wherein the pluralityof apertures are arranged at different diameters from a diametricalcenter of the carrier unit.
 18. The transfer case of claim 15, whereinthe apertures have an arc shape with a radially inner end and radiallyouter end, wherein the arc shape is concave in a radially outerdirection.
 19. The transfer case of claim 18, wherein the number ofapertures corresponds to the number of mounting holes.
 20. The transfercase of claim 19, wherein the apertures are disposed along a load pathextending between the teeth and the mounting holes to intercept a crackoriginating at the teeth and propagating toward the mounting holes.